The communication systems known as using an electro-magnetic field induced in the human body include a communication systems comprising a transmitter, in which voltage signals generated by modulating communication information is applied to the human body by capacitance coupling to induce an electric field in the vicinity of the human body, and a receiver, in which the strength of the electric field induced by the human body is detected and the strength of the electric field is demodulated into communication information (refer to patent documents 1, 2 and 3).
In these communication systems the electric field strength in the receiver is detected by coupling the electric field in the vicinity of the human body with electro-optic crystal via electrode located near the human body as changes in polarization characteristics of the electro-optic crystal (Patent documents 1 and 2), or from the output from FET (Field Effect Transistor) with its gate connected with the electrodes located under the electric field in the vicinity of the human body (Patent document 3).
[Patent Document 1]    Japanese Patent Application Laid-Open Publication No. 2001-298425
[Patent Document 2]    Japanese Patent Application Laid-Open Publication No. 2001-352298
[Patent Document 3]    Japanese Patent Application Laid-Open Publication No. 2004-282733